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Gravity waves on the water

Atmospheric gravity waves over the Persian Gulf

Rollercoaster airflow produces smooth and rough patches on the waters of the Persian Gulf. The effect is produced by "gravity waves".

When the Sun reflects off the surface of the ocean at the same angle that a satellite sensor is viewing the surface, a phenomenon called sunglint occurs.

In the affected area of the image, smooth ocean water becomes a silvery mirror, while rougher surface waters appear dark.

Sometimes the sunglint region reveals interesting ocean or atmospheric features that the sensor does not usually record.

The image above shows a large, overlapping wave pattern in the sunglint off the Persian Gulf.

The pattern is not from large ocean waves, however. It is the “impression” of atmospheric gravity waves on the surface of the ocean.

As the name implies, atmospheric gravity waves form when buoyancy pushes air up, and gravity pulls it back down, a bit like a rollercoaster. On its descent into the low-point of the wave (the trough), the air touches the surface of the ocean, roughening the water.

The long, vertical dark lines show where the troughs of gravity waves have roughened the surface. The brighter regions show the crests of the atmospheric waves.

Beneath the crests, the water is calm and reflects light directly back towards the sensor.

The image was captured by the MODIS instrument aboard NASA’s Terra satellite on June 14, 2010.

Adapted from information issued by Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC.